The ultimate aim of this research is to determine the cell lineages of the mammary gland which are the critical cells for morphogenesis, preneoplastic, and neoplastic transformation. The immediate specific aims of the experiments proposed herein are to determine cell phenotypic markers and growth properties for mammary cell lines and correlate these properties with morphogenesis and preneoplastic transformation in vivo. The recently described mammary cell line Comma-D will be used in these experiments. This established cell line in vitro exhibits normal morphogenesis when transplanted in vivo, is pseudodiploid, and is inducible for casein synthesis by specific hormones. Two other cell lines are non-transplantable in vivo. It is proposed to develop clonal cell populations from five mammary epithelial cell lines and determine which specific cell type(s) is critical for morphogenesis and preneoplastic transformation. (M)